Nucleic-Acid Amplification Test for STDs

A blood sample being held with a row of human samples for analytical testing including blood, urine, chemistry, proteins, anticoagulants and HIV in lab
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Nucleic-acid amplification tests, also known as NATs or NAATs, are used to identify small amounts of DNA or RNA in test samples. When it comes to STD testing, there are NATs available that can detect a variety of different STDs. In fact, most urine tests for STDs are performed using nucleic-acid amplification tests.

How Do Nucleic-Acid Amplification Tests Work?

There are several different kinds of nucleic-acid amplification tests, but they are all based on the same principle.

A NAT uses a series of repeated chemical reactions to make numerous copies of the DNA or RNA that doctors are trying to detect. These reactions amplify the signal of the nucleic acids in the test sample so that they are easier to identify. It's much simpler to find 10,000 copies of a gene than 10. 

What Does This Have to Do With STD Testing?

The process of amplifying bacterial or viral nucleic acids is not in itself the STD test. Instead, once the amount of DNA or RNA has been increased in the sample using PCR or LCR, more conventional tests are used to detect it. These tests usually involve some form of nucleic acid hybridization. In those tests, the sample is probed with an artificially produced complementary strand of DNA or RNA that has been labeled in some way that makes it easy to detect. It may help to picture it as a glow in the dark tag that only sticks to one very specific piece of identifying information.

Nucleic-acid amplification tests are incredibly useful for STD testing. They allow doctors to detect an STD pathogen even when only a very small number of organisms are present. It is this sort of technology that has made it possible to do urine testing for STDs that were previously only detectable by swab.

Furthermore, since nucleic-acid amplification tests are incredibly sensitive to even small amounts of viral DNA, they are very important for screening the blood supply. These tests make it possible to detect tiny amounts of HIV and other blood-borne pathogens that might otherwise be missed.

There are also non-amplified nucleic acid tests available for certain STDs, such as gonorrhea and chlamydia. Non-amplified nucleic acid hybridization tests are more likely to be used when large amounts of bacterial or viral DNA (or RNA) would be expected to be present, such as in a urethral swab or in a bacterial culture sample. In such circumstances, no amplification is necessary. In these samples, if DNA or RNA is present, it should be present in detectable amounts.

Example of This Test in Action

Nucleic-acid amplification tests are incredibly sensitive methods of detecting whether a bacteria or virus is present in a biological sample. When it comes to detecting genital herpes in a sore from a person who has symptoms, these tests serve as a viable alternative to a viral culture. Viral cultures can be difficult for some laboratories to perform. Unlike herpes blood tests, a NAT still involves the direct determination of whether a virus is present in the sample rather than looking for anti-herpes antibodies.

Nucleic-acid amplification has also allowed for an expansion of chlamydia and gonorrhea screening around the country. Now such screening can now be done on urine samples instead of requiring a urethral or cervicovaginal swab. It has thus become easy to test large numbers of young men and women for STDs in a variety of both clinical and non-clinical settings. Collecting urine requires no medical expertise, and people are more likely to be willing to pee in a cup than undergo a genital swab.

Researchers have also used nucleic-acid amplification tests to get more information about the extent of the problem of asymptomatic STDs in the United States.

Large-scale NAT-based screening programs have been implemented in the military, in urban teenagers, in men who have sex with men, and in other high-risk and low-risk groups. These tests allow for the detection of STDs in small samples that are often taken as part of large research studies on population health. 

Sources:

Bernstein KT, Chow JM, Pathela P, Gift TL. Bacterial Sexually Transmitted Disease Screening Outside the Clinic--Implications for the Modern Sexually Transmitted Disease Program. Sex Transm Dis. 2016 Feb;43(2 Suppl 1):S42-52. doi:  10.1097/OLQ.0000000000000343.

Chow EPF, Walker S, Read TRH, Chen MY, Bradshaw CS, Fairley CK. Self-Reported Use of Mouthwash and Pharyngeal Gonorrhoea Detection by Nucleic Acid Amplification Test. Sex Transm Dis. 2017 Oct;44(10):593-595. doi: 10.1097/OLQ.0000000000000654.

Trembizki E, Costa AM, Tabrizi SN, Whiley DM, Twin J. Opportunities and pitfalls of molecular testing for detecting sexually transmitted pathogens. Pathology. 2015 Apr;47(3):219-26. doi: 10.1097/PAT.0000000000000239.

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